Stains comprising mixtures of Methylene Blue and related thiazine dyes with Eosin are used routinely for the coloration of blood and bone-marrow films. These Romanowsky-type stains demonstrate the morphological features which distinguish the various haemopietic cells and those which characterize blood diseases. The term Romanowsky-type stain is commonly applied to any stain comprising Methylene Blue, its products of oxidation and a halogenated Fluorescein dye, usually Eosin Y. Successful Ramanowsky-type stains produce the Romanowsky effect. This may be defined as the condition in which the typical coloration of certain cell components results from the conbined action of a cationic and anionic dye, and cannot be produced by either dye acting along. It consists of the purple coloration of leucocyte chromatin and neutrophil granules and the magenta or carmine coloration of the nuclei of parasitic Protozoa. This effect is described as the result of some interaction of Azure B (an oxidation product of Methylene Blue) and Eosin Y by P. N. Marshall in his review of Romanowsky-type Stains in Haemotology appearing in Histochemical Journal 10 (1978) Pp. 1-29. This article also describes the phenomena of ageing the dye to cause it to stain mast cell granules red and the theory that Methylene Blue ages in solution to give some new dye which produces the proper staining. The requirement that the dye be aged was circumvented by boiling a solution of Methylene Blue with potassium carbonate to provide what became known as polychrome Methylene Blue. Wright's stain, extensively used in the United States, is a Romanowsky stain solution in which the Methylene Blue is polychromed by one or more known techniques and the product then mixed with Eosin Y. Polychroming results in a complex mixture of dyes including Azures B, C and A as well as leaving some Methylene Blue starting material in the final mixture. Marshall reports two disadvantages inherent in the polychroming of Methylene Blue. One is that the procedure results not only in the production of dyes essential for Romanowsky-type staining, but also in certain extraneous ones. He also states that the stain is not suitable for reproducible production on a commercial scale because polychroming cannot be effectively controlled on such a scale. The Marshall article reports the recent development of a reproducible stain suitable for commercial exploration, which avoids the polychroming process being comprised of purified Azure B and commercial Eosin Y whose methanolic stock solutions are prepared separately and mixed just prior to staining. These dye solutions are prepared separately and mixed just prior to use because the admixture of solutions of Azure B and Eosin Y results in the rapid formation of a precipitate which quickly renders the stain unsuitable for the intended purpose. It also appears that, in the typical Romanowsky-type stain, the Methylene Blue slowly oxidizes to Azure B and that the combination of Azure B and Eosin Y accounts for the desirable staining properties. The oxidation process will also continue in a sequence which will form other azure products that are not essential for staining but reduce the Azure B concentration. The Azure B formed by the gradual oxidation will form a reaction product with Eosin Y which precipitates from solution, but this precipitation is not as catastrophic as when Azure B and Eosin Y are combined directly in solution because of the gradual oxidation of Methylene Blue to Azure B. It would be desirable to provide a stabilized solution of Azure B and Eosin Y which would exhibit a reasonable shelf-life in order to aviod the step of mixing the separate solutions just before their use. U.S. Pat. No. 4,290,769, issued Sept. 22, 1981, discloses the stabilization of a Romanowsky-type stain solution comprising Methylene Blue, polychromed Methylene Blue products (azures) and an eosin dye with an alkylamine hydrohalide. Diethylamine hydrochloride is described as being a useful stabilizer for this three-component polychromed stain system. Unexpectedly, we have discovered that diethylamine hydrochloride is a suitable stabilizer for the much more unstable two-component system of Azure B and Eosin Y in methanolic solution.